Protection system for turbo-generator starters

ABSTRACT

A system for preventing operation of an electric starter for a gas turbine engine if such operation would be hazardous to the starter gearing, includes a time delay mechanism, or speed sensing device, which overrides the normal starter actuator under hazardous conditions.

United States Patent Pelabon Oct. 15, 1974 1 PROTECTION SYSTEM FOR 3,394,618 7/1968 Dhonau 105/615 TURBO GENERATOR STARTERS 3,577,001 5/1971 Cummins 290/38 R 3,594,029 7/1971 Holt 290/38 R [75] Inventor: And e E- Pelabo a s, France 3,712,283 1/1973 Kiess ct a1 290/38 R Assignee: ANF Fraugeco q Courbevoie 3,714,450 1/1973 Sawyer ct a1 290/38 R Hauts de Seine, France f Primary ExaminerRobert K. Schae er I F'Ied: 1973 Assistant ExaminerM. Ginsburg [21] App]. No.: 350,815

[57] ABSTRACT [52] US. Cl. 307/116, 290/38 R 51 1 1111. C1. 1102b 1/00 A System KP1Y l9 P i Stan" [58] Field of Search 307/116 112 113- gas turbine engme If such operam be ,5 R hazardous to the starter gearing, includes a time delay mechanism, or speed sensing device, which overrides [56] References Cited the normal starter actuator under hazardous condi- UNITED STATES PATENTS 2,062,970 12/1936- Dyer 290/37 R 8 Claims, 4 Drawing Figures STARTER CIRCUIT I DELAY I 7 21 10 TURBINE SHUT-OFF CIRCUIT PAIENI um I 5 I974 I saw 1 or 2 STARTER TURBINE SHUT-OFF CIRCUIT STARTER S CI PROTECTION SYSTEM FOR TURBO-GENERATOR STARTERS The present invention concerns a protection system designed to prevent wear and tear on the electric starter of a gas turbine thermal engine directly coupled to an alternator of an electric power-generating system.

In existing power-generating systems comprising an alternator and a gas turbine, the electric starter for the turbine, usually of the Bendix type, includes a pinion which meshes with a gear wheel connected to the turbine shaft during start-up only, which pinion is efficiently protected against overload, but has no protection in the event of start-up closely following either a voluntary or involuntary shut-off of the turbine.

In fact, when the turbine is shut off by the discontinuing of fuel injection, for example, because of the inertia of the alternator and the almost total lack of friction on the shaft of the linked turbine and the alternator, the rotary speed of this shaft decreases very slowly. If the start-up signal is given while the turbine-alternator shaft, hence the gear wheel actuated by the starter, is still rotating at high speed, the starters working pinion cannot mesh with the cogged crown or, if it does mesh, the starter proceeds to rotate at unduly high speed and is therefore instantly damaged.

The purpose of the present invention is to remedy this defect and to protect the starter by preventing its actuation again until the speed of the turbine shaft has dropped below a-given value, known as the maximum speed, below which the meshing of the starter can occur without damage to itself, or the starting pinion.

. The time I required by the turbine shaft to drop down from its normal running speed to the safe speed defined above is practically constant, since this time t depends solely on shaft friction.

To, this end, in an initial concept of the invention, protection of the starter can be achieved by preventing turbine start-up during a time t following the actuation of the turbine stop signal, and this is achieved by means of time delay relays.

In a second concept of the invention, and in an initial case, turbine shaft speed can be detected, or sensed, by either electrical or mechanical means, and the turbine s start up actuator can be overridden until the speed detected is less than the maximum safe speed. This is achieved mechanically via a centrifugal or pendular regulator connected to the turbine shaft and driving a contact.

In anothercase, it is achieved electrically, via an electronic tachometer detector connected to the turbine shaft one contact of which prevents start-up at a speed above the maximum safe speed.

A clearer understanding of the invention is provided by the following written description and annexed drawings, which show, as a nonlimitative example, the application of a protective system enabling prevention of deterioration to the electric starter of a directly coupled turbine thermal engine driving the alternator of a power generating system. i

In the drawings,

FIG. 1 is a schematic side elevation of a preferred form of starter protecting system according to the invention utilizing time delay means;

FIG. 2 is a view of a modified portion of the invention, employing a centrifugal governor;

FIG. 3 is a schematic view of another modified portion which utilizes an electronic tachometer, and;

FIG. 4 is a schematic diagram of a simplified form of circuit for the starter circuit of FIG. I.

In the FIGS. 1 3, a conventional thermal gas turbine engine is denoted generally by numeral 10, having an air intake duct 11 and an exhaust duct 12, both of which lead to the exterior of a vehicle (not shown). The forward end of the main shaft of the turbine is provided with a pinion 13 which meshes with a gear 14 mounted on a stub shaft which also includes another pinion gear 15 connected to drive the gear 16 on one end of the drive shaft of an electric alternator, indicated generally by numeral 17.

An electric starting motor 18, which may be attached to the housing containing the aforementioned gearing, is provided with a conventional pinion 19, which is axially shiftable, by means which are well-known in the art such as a Bendix spring, between a disengaged position as shown and a second position to mesh with one of the gears in the train such as the main gear I6 for starting the turbine 10. As soon as the fuel is sufficiently ignited in the turbine to assure its continued operation, the gear 19 automatically returns to its firstposition. Ordinarilly, this takes place at a speed which is somewhat less than the turbines running speed and, it is obvious that, once disengaged, and with the starter at rest, reengagement of the starting gear would strip the teeth of these two gears, or literally tear-up" the starter motor itself, if this re-engagement occurred while the turbine was running at anything approaching normal speed.

While the starting motor can be manually controlled by a simpleswitch connected in circuit with a source of electricity, in one form of the invention the energization of the starter is accomplished automatically as one of a programmed sequence of events connected with the starting operation of the turbine which sequence is accomplished by manual operation of a push button connected in the starting circuit indicated by numeral 20. While not limited in this respect, one form of programmed circuit is disclosed in my copending application, Se'r. No. 350,814 filed concurrently herewith.

Since the alternator and turbine are directly coupled at all times, and only the friction of the moving parts imparts any load on the system when the fuel supply to the turbine is shut off, the slowing down of the turbine is fairly predictable, and a time t can be calculated, which will be sufficient to ensure that the speed of the gearing will be sufficiently low for safe engagement of the starting gear. Therefore, the circuit 20 includes a time delay relay means, indicated by numeral 21. The operation of relay 2] is initiated by the shut-off circuit for the turbine, indicated generally by numeral 22. While the shut-off circuit might consist of a simple valve to close the fuel supply line and simulataneously energize the delay relay, it is preferable to perform a sequence of operations in addition to cutting off the main fuel supply, all of which are performed by circuit 22 in response to manual operation of a push-button.

The function of delay circuit 21 is to override, or prevent, the normal sequencing operations of the starting circuit 20, even if an attempt is made to set these operations in motion, until a time interval r has elapsed after actuation of shut-down circuit 22. As soon as this time has elapsed, indicating that operation of the starter will not be hazardous, delay relay 21 reactivates the starter circuit 20.

A specific example of starting and stopping circuit arrangement exemplified by the circuits 20, 21 and 22, is shown in FIG. 4, in which numerals 30 and 31, respectively denote manually actuated start and stop push button switches, connected by wire 32 to one side of a source of electrical energy, which also supplies a relay 33. The push button switch 30 is of the self-maintained type, so that when the operator momentarily actuates switch 30, the result is to energize relay 34, through normally closed relay switch 35. At the same time, the self-maintaining action of switch 30 automatically closes switch 39 so that relay 34, which actuates a sequence of operations involved in the starting of the turbine 10, will remain energized until the starting sequence is completed.

However, if the stop switch 31 is actuated at any time, this will energize relay 36 which initiates the sequence of operations for stopping the turbine, which mayonly consist of shutting the fuel valve. Relay 36 also closes the'normally open switch 33, which energizes relay 38 and this, in turn, closes switch 37 and opens switch 35. Relay 38 is a time delay switch, adjusted to remain energized for the period of time t which is known to be required for the alternatorturbineto slow down to a safe speed for starter engagementaThus, while the stop switch-31 may beonly momentarily actuated to close switch 33, the resulting closing of switch'37 ensures that relay 38 will remain energized for the full time period. Concurrently, switch 35 will also remain open during this time period, so that actuation of start switch 30 cannot possibly energize relay 34 to initiate the turbine starting sequence.

ln'theform of the invention shownin FlG. 2, a centrifugal governor means, indicated generally by numeral 23 is arranged to be driven by an element of the rotating system; such as the gear 14. This governor means includes an electrical switch 24 which is controlled to close acircuit 25, connected with a starter circuit 26, which'may consist of .a simple push button electric switch connected in series with switch 24 to energize the starter by connecting it to a source of electrical energy, such as a battery, through wire 27. Obviously, if the energizing switch contained in circuit 26 is actuated, either manually or by some automatic sequencing system, at any time that the turbinealternator shafts are turning at a rate of speed which causes switch 24 to be in its open condition, no current will flow in wire 27 and no engagement of start gear 19 can take place. Thus, the governor means 23 is effective to override any action of starter circuit 26 until such time as the alternator-turbine rotation has been reduced to a speed that allows switch 24 to close, regardless of the length of time involved.

FIG. 3 illustrates another modification which is similar to that of FIG. 2 except for the fact that the governor means, indicated generally by numeral 28, comprises an electronic tachometer means which is connected into starter circuit 29 to override that circuit at such times as the alternator-turbine rotation exceeds a speed which would be hazardous to the actuation of starter l8. ln the form shown, the governor means 28 comprises an electrical generator driven, as before, by gear 14 togenerate an electrical signal whose value (such as voltage, current, or frequency) varies in proportion to speed. This energy may be fed to the starter circuit 29 to override any other device employed to energize the starter through wire 27. For example, the energy from tachometer 28 could be used to control a solenoid switch, or to control solid state devices to prevent energization of wire 27 when the turbine shaft exceeds the safe limit. Other forms of electronic tachometers, including solid state devices, could be substituted by the generator shown. Devices of this type, including those which sense rotation by counting the frequency of repetitive movements in a machine, or changes of pressure or temperature related to rotational speed, are well known in the art and need not be specifically described.

I claim:

I. A protective system for the electric starter means of a gas turbine engine which is directly coupled to an electrical generator, said gas turbine engine being of the type wherein starting is accomplished by a first sequence of operations which includes the energization of an electrical starting motor for engaging a pinion with gearing connected with a turbine shaft, the engagement to be accomplished only when the turbine engine is stopped or running at less than a predetermined speed, and stopping of the turbine is accomplished by a second sequence of operations, circuit means includingfirst manually operable switch means for initiating said first sequence of operations, second manually operable switch means for initiating said second sequence of operations, said circuit means including control means responsive to operation of said second switch means for preventing initiation of said first sequence of operations by said first switch means unless said turbine engine is in a condition for engagement of said pinion with said gearing.

2. The invention defined in claim 1, wherein said control means includes time delay means responsive to operation of said second switch means.

3. The invention defined in claim 1, wherein said control means includes centrifugally controlled electrical switch means responsive to the speed of rotation of said turbine engine.

4. The invention defined in claim 1, wherein said control means includes electrical tachometer means responsive to the speed of rotation of said turbine engine.

5. The invention defined in claim 1, wherein said control means includes electrically energized time delay switch means responsive to operation of said second switch means to prevent initiating of said first sequence of operations by said first switch means until the elapse of a predetermined period of time.

6. The invention defined in claim 5, wherein said first manually operable switch means is operable to close a normally open first circuit included in said circuit means and said time delay switch means includes a normally closed switch connected in series with said first manually operable switch means and is responsive to said second manually operable switch means to open said first circuit for said predetermined period of time.

7. The invention defined in claim 6, wherein said time delay switch means is connected in a second circuit included in said circuit means, for energizing said time delay switch means, said second circuit including two normally open switches connected in parallel, one of said switches being responsive to operation of said 0nd manually operable switch means is operable to close a normally open third circuit included in said circuit means, said third circuit including a relay energized by closure of said third circuit, said one normally open switch in said second circuit being closed by energizing of said relay. 

1. A protective system for the electric starter means of a Gas turbine engine which is directly coupled to an electrical generator, said gas turbine engine being of the type wherein starting is accomplished by a first sequence of operations which includes the energization of an electrical starting motor for engaging a pinion with gearing connected with a turbine shaft, the engagement to be accomplished only when the turbine engine is stopped or running at less than a predetermined speed, and stopping of the turbine is accomplished by a second sequence of operations, circuit means including first manually operable switch means for initiating said first sequence of operations, second manually operable switch means for initiating said second sequence of operations, said circuit means including control means responsive to operation of said second switch means for preventing initiation of said first sequence of operations by said first switch means unless said turbine engine is in a condition for engagement of said pinion with said gearing.
 2. The invention defined in claim 1, wherein said control means includes time delay means responsive to operation of said second switch means.
 3. The invention defined in claim 1, wherein said control means includes centrifugally controlled electrical switch means responsive to the speed of rotation of said turbine engine.
 4. The invention defined in claim 1, wherein said control means includes electrical tachometer means responsive to the speed of rotation of said turbine engine.
 5. The invention defined in claim 1, wherein said control means includes electrically energized time delay switch means responsive to operation of said second switch means to prevent initiating of said first sequence of operations by said first switch means until the elapse of a predetermined period of time.
 6. The invention defined in claim 5, wherein said first manually operable switch means is operable to close a normally open first circuit included in said circuit means and said time delay switch means includes a normally closed switch connected in series with said first manually operable switch means and is responsive to said second manually operable switch means to open said first circuit for said predetermined period of time.
 7. The invention defined in claim 6, wherein said time delay switch means is connected in a second circuit included in said circuit means, for energizing said time delay switch means, said second circuit including two normally open switches connected in parallel, one of said switches being responsive to operation of said second manually operable switch means to close said second circuit for energizing said time delay switch means, the other of said normally open switches being responsive to energizing of said time delay switch means to also close said second circuit only so long as said time delay switch means is energized.
 8. The invention defined in claim 7, wherein said second manually operable switch means is operable to close a normally open third circuit included in said circuit means, said third circuit including a relay energized by closure of said third circuit, said one normally open switch in said second circuit being closed by energizing of said relay. 